Interstitial cystitis (IC) is a chronic, debilitating clinical syndrome presenting as urinary urgency, frequency, and/or pelvic pain in the absence of any known cause. The etiologic mechanisms underlying IC are poorly understood and although epithelial dysfunction, abnormal mast cell activity, and nerve damage have all been implicated in IC, the importance of each of these factors has not been delineated and is still in dispute. We propose that genetic mechanisms underlie most of the symptoms that patients with IC experience. We present several lines of evidence for this conclusion, including data for familial clustering of IC in 20 Bulgarian Roma families and significant preliminary evidence for linkage on chromosome 1 in two nuclear families with numerous members affected with IC. High-density mapping in large families has provided a relatively short list of positional candidate IC genes, and direct sequence analysis of these genes will reveal the causative mutation(s) underlying familial IC. Identification of IC susceptibility genes should provide insight into the molecular mechanisms and pathways that underlie the disease. Furthermore, we have evidence for the presence of anti-proliferative factor (APF) activity in the affected family members and lack of APF activity in the unaffected individuals, indicating that familial IC is correlated with the same urine biomarker profile found in sporadic IC. This suggests the results from our genetic studies will be immediately relevant to the general IC community. In this proposal we will pursue the following specific aims: Aim 1. Collect DNA samples from multigenerational families of Bulgarian Roma with autosomal dominant inheritance of IC. Aim 2. Perform high density linkage analysis in the most informative pedigrees using the Affymetrix GeneChip Human Mapping 10K Array to establish genetic linkage between the IC phenotype and DNA polymorphic markers in those families. Aim 3. Identify and verify a gene in which mutations cause IC by direct sequencing of positional candidate genes. Aim 3a. Search for a mutation in a gene in the interval defined by the linkage peak. Since linkage peaks suggest that the disease gene is in the proximity of the peak, we will perform mutation screening in the candidate interval using gene sequencing. This will allow the identification of mutations causing IC. Aim 3b. Expand the analysis of the candidate gene(s) in families from the US. To validate our identification of a candidate IC gene, we will look for additional mutations in a select group of families from the US of non-Bulgarian ancestry.